Machine type communication (MTC) refers to a communication scheme between one or more machines and is also referred to as machine-to-machine (M2M) communication. Here, a machine refers to an entity which does not require direct human operation or intervention. For example, a device including a mobile communication module, such as a meter or a vending machine, may include a user equipment such as a smartphone which is capable of automatically accessing a network without operation/intervention of a user to perform communication. Various examples of such a machine are referred to as an MTC device or terminal in the present specification. That is, MTC refers to communication performed by one or more machines (that is, MTC devices) without human operation/intervention.
MTC may include communication (e.g., device-to-device (D2D) communication) between MTC devices and communication between an MTC device and an MTC application server. Examples of communication between an MTC device and an MTC application server include communication between a vending machine and a server, communication between a point of sale (POS) device and a server and an electric meter, and communication between a gas meter or a water meter and a server. AN MTC-based application may include security, transportation, healthcare, etc.
Meanwhile, if congestion or overload occurs in a network, congestion control may be performed in a control plane. For example, network congestion control may be performed at a non-access stratum (NAS) level which is an uppermost stratum in a control plane between a terminal and a network control node in a radio interface. In general, if a network congestion occurs, a network may configure a back-off timer for inhibiting a request for a network for a predetermined time with respect to a terminal.
According to operation of a currently defined wireless communication system, priority may be configured per terminals, and only one of “(NAS signaling) low priority” for a terminal supporting MTC or “(NAS signaling) non-low priority” for a terminal supporting non-MTC.
Meanwhile, if network congestion or overload occurs, a back-off timer (BOT) may be used in order to distribute network load. Back-off timers may be classified into a Mobility Management (MM) back-off timer and a Session Management (SM) back-off timer. MM back-off timer defines a time in which a terminal is prohibited from performing MM-related operations such as an attach request, SM back-off timer defines a time in which a terminal is prohibited from performing SM-related operations such as a session establishment/modify request related to an Access Point Name (APN).